气体对氮化钽热场阴极发射特性的影响

EFFECT OF GASES ON EMISSION CHARACTERISTICS OF THE Ta_2N THERMAL FIELD ELECTRON CATHODE

氮化钽(Ta_2N)热场发射阴极有低、高两种发射状态。在这种阴极不馈有电压也不加温情况下,于一定时间内分别曝露于氧、氮、氧等微量气体中,实验结果表明这对其场发射特性无明显影响。在馈有电压并加温到1290℃以上情况下,当注入气体分压强达10^(-4)Pa量级时,气体种类不同,氧化钽场阴极的特性有不同的变化:对于氧,其场发射电流变化最大,并在场发射图象中增添出现了两个相应于(100)和(010)等晶面发射的“氧特征点”,其亮度超过了相应于(111)、(112)等晶面的亮点;对于氮,场发射电流约有20%的增高,场发射图象也略有变化,但仍以(111)等晶面发射为主;对于氢,场发射电流和图象均无明显改变。最后,还对气体影响氮化钽热场阴极发射特性的机理进行了讨论。

Ta_2N thermal field(TE) emission has been investigated under both I, w and high emission states. The emission characteristics of TF cathode are not effected by the exposure of a small amount of O_2, N_2or H_2 gases for a certain period when the cathode is not heated and operating voltage is not applied. However, the emission characteristics of Ta_2N TF cathode shows changes if O-2, N_2orH_2 is introduced up to a partial pressure of about 10^(-4)Pa when the cathode is heated to a temperature higher than 1290℃ and operating voltage is applied, when O_2 is added, the FE current shows most significant change, Two additional 'spots' corresponding to (100), (010) Planes appear on its FE pattern. These 'spots' are even brighter than the 'spots' corresponding to (111),(112) and other planes. The FE current increase by about 20% when N-2 is added, The FE patternalso changes somewhat, but the 'spots' corresponding to (111) planes are still the brightest ones. For added H_2, neither FE current nor emission pattern show significant change. In additions to the experimental results, also discussed is the mechanism which explains how the gases affect the emission characteristics of Ta_2N TF cathode.